The invention relates to devices and methods for removing tissue from body passageways, such as removal of atherosclerotic plaque from arteries, utilizing a rotational atherectomy device.
A variety of techniques and instruments have been developed for use in the removal or repair of tissue in arteries and similar body passageways. A frequent objective of such techniques and instruments is the removal of atherosclerotic plaques in a patient""s arteries. Atherosclerosis is characterized by the buildup of fatty deposits (atheromas) in the intimal layer (under the endothelium) of a patient""s blood vessels. Very often over time, what initially is deposited as relatively soft, cholesterol-rich atheromatous material hardens into a calcified atherosclerotic plaque. Such atheromas restrict the flow of blood, and therefore often are referred to as stenotic lesions or stenoses, the blocking material being referred to as stenotic material. If left untreated, such stenoses can cause angina, hypertension, myocardial infarction, strokes and the like.
Rotational atherectomy procedures have become a common technique for removing such stenotic material. Such procedures are used most frequently to initiate the opening of calcified lesions in coronary arteries. Most often the rotational atherectomy procedure is not used alone, but is followed by a balloon angioplasty procedure, which, in turn, is very frequently followed by placement of a stent to assist in maintaining patentcy of the opened artery. For non-calcified lesions, balloon angioplasty most often is used alone to open the artery, and stents often are placed to maintain patentcy of the opened artery. Studies have shown, however, that a significant percentage of patients who have undergone balloon angioplasty and had a stent placed in an artery experience in-stent restenosisxe2x80x94i.e., blockage of the stent which most frequently develops over a period of time as a result of excessive growth of scar tissue within the stent. In such situations an atherectomy procedure is the preferred procedure to remove the excessive scar tissue from the stent (balloon angioplasty being not very effective within the stent), thereby restoring the patentcy of the artery.
Several kinds of rotational atherectomy devices have been developed for attempting to remove stenotic material. In one type of device, such as that shown in U.S. Pat. No. 4,990,134 (Auth), a burr covered with an abrasive cutting material such as diamond particles is carried at the distal end of a flexible drive shaft. The burr is rotated at high speeds (typically, e.g., in the range of about 140,000-180,000 rpm) while it is advanced across the stenosis. As the burr is removing stenotic tissue, however, it blocks blood flow. Once the burr has been advanced across the stenosis, the artery will have been opened to a diameter equal to or only slightly larger than the maximum outer diameter of the burr. Frequently more than one size burr must be utilized to open an artery to the desired diameter.
U.S. Pat. No. 5,314,438 (Shturman) shows another atherectomy device having a drive shaft with a section of the drive shaft having an enlarged diameter, at least a segment of this enlarged diameter section being covered with an abrasive material to define an abrasive segment of the drive shaft. When rotated at high speeds, the abrasive segment is capable of removing stenotic tissue from an artery. Though this atherectomy device possesses certain advantages over the Auth device due to its flexibility, it also is capable only of opening an artery to a diameter about equal to the diameter of the enlarged diameter section of the drive shaft.
Co-pending U.S. patent application Ser. No. 08/911,586, filed Aug. 14, 1997, describes a rotational atherectomy device having a flexible, elongated, rotatable drive shaft with an eccentric enlarged diameter section. At least part of the eccentric enlarged diameter section has a tissue removing surfacexe2x80x94typically an abrasive surfacexe2x80x94to define a tissue removing segment of the drive shaft. When placed within an artery against stenotic tissue and rotated at sufficiently high speeds (e.g., in the range of about 20,000 rpm to about 200,000 rpm) the eccentric nature of the enlarged diameter section of the drive shaft causes such section to rotate in such a fashion as to open the stenotic lesion to a diameter substantially larger than the outer diameter of the enlarged diameter section. Preferably the eccentric enlarged diameter section of the drive shaft has a center of mass spaced radially from the rotational axis of the drive shaft, facilitating the ability of the device to open the stenotic lesion to a diameter substantially larger than the outer diameter of the enlarged diameter section. Typically this is achieved by constructing the enlarged diameter section of the drive shaft asymmetricallyxe2x80x94i.e., spacing the geometric center of the eccentric enlarged diameter section of the drive shaft away from the rotational axis of the drive shaft. A drive shaft having an eccentric enlarged diameter tissue removal section with a diameter of not more than 2 mm is capable of opening stenotic lesions to a diameter equal to the original diameter of the main coronary arteries (i.e., to a diameter of more than 3 mm) so that in a significant percentage of cases balloon angioplasty may not be needed to complete the procedure. The device is particularly useful for cleaning out partially blocked stents.
The invention provides an improved method of manufacturing a drive shaft having an asymmetrical tissue removal section. One or more strands of wire are helically wound about an elongated mandrel having an enlarged diameter section with a predetermined shape, thereby forming an elongated, flexible drive shaft which has an enlarged diameter tissue removal section defined by wire turns of the drive shaft and having an initial shape which corresponds to the shape of the enlarged diameter section of the mandrel. A portion of the drive shaft, including the enlarged diameter tissue removal section, is placed into a first clamp and heat treated (the xe2x80x9cfirst heat treatmentxe2x80x9d) to give the wire turns of the enlarged diameter tissue removal section an initial set, thereby preserving the initial shape of the enlarged diameter tissue removal section of the drive shaft.
The drive shaft is then removed from the first clamp and at least the enlarged diameter tissue removal section of the drive shaft is immersed into a solution of nitric acid to dissolve at least the enlarged diameter section of the mandrel from within the drive shaft (preferably the entire drive shaft is so immersed, thereby dissolving the entire mandrel).
The enlarged diameter section of the drive shaft is then deformed to an asymmetrical shape by placing a portion of the drive shaft, including the enlarged diameter tissue removal section, into a second clamp. The clamped portion of the drive shaft is then heat treated for a second time (the xe2x80x9csecond heat treatmentxe2x80x9d) to give wire turns of the enlarged diameter tissue removal section a new set, thereby preserving the asymmetrical shape of the enlarged diameter section.
Preferably the deformation of the enlarged diameter tissue removal section to its asymmetrical shape is such that in its desired shape the enlarged diameter tissue removal section has a longitudinally flat xe2x80x9csidexe2x80x9dxe2x80x94i.e., all wire turns of the tissue removal section may be connected by an imaginary straight line which throughout its length is parallel to the rotational axis of the drive shaft. This shape of the tissue removal section of the drive shaft is even more asymmetrical than the tissue removal section of the device described in application Ser. No. 08/911,586 referred to above, thereby facilitating faster opening of stenotic lesions to an even larger diameter.